1. Field of the Invention
The invention is generally related to the removal of sulfur-containing compounds from flue gases, and more particularly to the use of air sparging for the oxidation and/or mixing and suspension of such compounds.
2. General Background
Industrial combustion systems, such as power plant boiler combustion chambers, that use high sulfur fuels tend to release sulfur-containing compounds such as sulfur dioxide and sulfur trioxide into the flue gases. Due to the detrimental effects of such compounds, it is necessary to prevent their release into the surrounding environment. Wet scrubbers for the desulfurization of flue gases treat the flue gas in a scrubbing tower with a scrubbing solution which may contain substances capable of binding the sulfur compounds. A reaction tank or recirculation tank at the bottom of the tower is used to collect the scrubbing solution, sulfur compounds removed from the flue gases, and any particulates scrubbed from the flue gases. The volume of the tank permits several chemical and physical processes to approach completion. Air sparging is an economical and simple means of providing oxidation air and mixing to a flue gas desulfurization system. The advantages of air sparging include low capital cost, control of the size of the air bubbles, even distribution of the air in the tank, and violent mixing between the air and the tank contents. A drawback of this method is the back flow of slurry into the sparge pipes and the potential blockage of the sparge pipe holes if the air flow is interrupted. Other systems include introducing the air in front of a rotating mixer to break the air bubbles, or introducing the air through the mixer shaft, which requires additional power to operate the mixers. In such systems, the loss of a mixer affects the capacity of the system to achieve oxidation unless a spare mixer is provided. Patents in this general area of technology that applicants are aware of include the following.
U.S. Pat. No. 4,515,754 to Stehning discloses a back wash means to circulate solids from the tank and mix them back in another elevation of the same tank. The function of back wash is to keep the solids in the tank mixed and in suspension.
U.S. Pat. No. 3,260,036 to DeBellis discloses a U-shaped trap to maintain a minimum liquid level in the tank equal to less than the height of the U bend.
U.S. Pat. No. 4,799,941 to Westermark discloses a method for condensing flue gases in combustion plants.
U.S. Pat. No. 1,940,199 to Wagner discloses a dust extractor wherein an inverted U-shaped trap is used to maintain a liquid level in the extractor when a drain valve is closed.
U.S. Pat. No. 2,403,545 to Nutting discloses a liquid level control apparatus for a dust collector wherein water is set by the hydraulic interaction of the air and water.
The existing art does not adequately address the slurry infiltration problem encountered in the reaction tank.